1. Field of the Invention
The present invention relates to a lead-frameless power inductor and method for fabricating the same, and more particularly to a lead-frameless power inductor which is fabricated in a whole set instead of being fabricated in the individual unit as that is conducted in the conventional way of production so as to promote the production efficiency and curtail the production cost, and at the same time, improve reliability of the electrical is connection between the power inductor produced as such with the external conductor terminals.
2. Description of Prior Art
Referring to FIG. 1A through 1D, which are the drawings of U.S. Pat. No. 6,204,744B1. In the drawings, a coil 10 which is attached to a circuit board 12, has an enclosure 14. From the enclosure 14 there extend a first conductor 16 and a second conductor 18 each respectively welded to welding pads 20 and 22. The coil 10 is a helical winding body 24 with multiple turns 30 of an erected rectangular cross sectional flat wire. The coil 10 includes an inner side end 26 and an outer side end 28, and a lead frame 32 is attached to the winding body 24 with its two terminals 34 and 38 each respectively welded to the inner side end 26 and the outer side end 28 of the winding body 24. Afterwards the winding body 24 with both welded conductors 16, 18 is set in a mold, and then the mold filled with preferably, a colloidal magnetic powder. After the magnetic powder is dried and hardened, the lead frame 32 is severed and taken away. The finished product of the inductor of the invention is obtained.
However, the inductor fabricated according to U.S. Pat. No. 6,204,744B1 has the following flaws, namely:    1. Using the flat wire as a winding element with two is external free end terminals is technically quite difficult to perform winding work.    2. As shown in FIG. 1D, if a round wire is used to wind up the coil 10, the coil 10 containing multiple layers of round wire element will increase the fabrication cost, and by no means meet the basic requirements of light, thin, short, compact which the present day electric products are asking for.    3. In the procedure of the fabrication, the conductors are at first welded to the coil body, and then the entire structure is put into the mold, and finally the magnetic powder is filled into the mold. In this way the perfect adhesiveness of the enclosing magnetic powder with the coil body and compactness of the whole inductor structure cannot be expected.    4. As the winding number of turns increases, the loosing of the inductance is severe owing to the electro-magnetic interference among the layers of coil element.    5. One by one fabrication process as that conducted at present leads to a great loss of manpower and time with a result of low production efficiency. In the fabrication, the two ends of the coil are at first welded to the corresponding two supporting legs of the lead frame, and the connecting conductors are cut after completing the fabrication to separate the lead frame. This also is causes the loss of material and increase of the fabrication cost.    6. In a traditional power inductor, the way of connection of the inductor to the outer conductor terminals belongs to a point-to-point contact. In this manner, when the power inductor is used under the circumference in which the temperature is violently changed or loaded for a long time, the coil body and the outer electrical terminals may be easily disconnected causing an accidental open circuit, or moreover, a burn down of the load side electronic product.
For these defects noticeable on the prior art, an improvement is seriously required. The inventor has dedicated great efforts for years to studying and improving these defects and finally come out with the present invention.